1. Field of the Invention
The present invention relates to stacking machines for printed products, and more particularly to a system and method for processing a stream of printed products arriving in an imbricated, or partially overlapping, stream into successive stacks.
2. Description of the Related Art
Printed products (also referred to as "products"), such as books, newspapers, magazines and pamphlets are produced in a printing, binding or collating business. Printing presses provide printed product to delivery equipment, such as conveyers or continuous moving belts, in an imbricated, or partially overlapping stream where the delivery equipment is maintained at a constant speed of up to 70,000 copies per hour. The delivery equipment frequently leads to a stacking machine where a preset number of products forms a stack and becomes ready for further processing or transportation.
The stacking machine may include an assembly to collect the product, an assembly to then process the collected stack, such as rotation or compression, and finally an assembly to push the stack out for further disposal. These steps are repeated in rapid cycles as long as product is delivered to the stacking machine by the conveyor. With the stacking machines known today, a minimum of about one second is necessary to dispose of a finished stack. During this one second interval, given present maximum delivery speeds, 19 products pass a given point in the stream and must therefore be stacked.
The present stacking machines are sufficient if it is desired to only make stacks of more than or equal to a certain quantity, which is dependent on the conveyor speed, e.g., 19 at a speed of 70,000 copies per hour. Furthermore, current stackers can provide a stack less than this number, or a low quantity stack, so long as the next stack to be made is not also a low quantity stack. However, there is a problem when stacks of low quantity need to be made continuously because disposing of one full stack cannot be completed fast enough for a stacking machine to cycle for another disposal cycle. This problem is highlighted whenever two or more stacks of low quantity are necessary in succession, such as in the case of when a mail sorting line encounters consecutive, sparsely populated zip codes.
Books, newspapers, magazines, pamphlets, and so forth, having folded or stapled sheets, or a combination thereof, typically have one edge which is somewhat thicker than the other edges. When such products are stacked in the same orientation, the connected edges build up faster than the free edges to a point where the stack is unstable and difficult to handle. A compensating stacker, such as the one disclosed in U.S. Pat. No. 4,547,112, which includes a temporary product holding assembly, a revolving platform, a compression assembly, and a pusher assembly, is used to mitigate this height differential. The temporary product holding assembly collects a temporary stack of products from a continuous infeed supply while the pusher moves a completed stack from the platform or while a partial work stack is compensated. The compensation step compresses the connected edges to flatten the stack of products and offsets successive layers by rotating the platform.
In the compensating stacker disclosed in the '112 patent, the temporary product holding assembly is disposed directly above the platform and is formed by a plurality of tines connected with rotatable shafts. After a predetermined number of products has been collected on the temporary holding assembly, the products are dropped onto the platform and a set of retractable compression rods is extended over the platform. The temporary product holding assembly then returns to a collecting position for receiving further products. The platform is thereafter raised to press the products on the platform against the retractable compression rods extended over the platform resulting in a flattening of the relatively thicker, connected edge of the products. While the products are being pressed against the compression rods, the platform is rotated through up to 180.degree. from its initial position. This rotation results in the relatively thick edges of the products in one portion of the stack being offset from the relatively thick edges of products in another portion of the stack. When a stack on the platform has the desired number of products, the pusher is actuated to push the stack from the platform for further handling, e.g., tying, wrapping, boxing, labelling. Since the stacker can stack products of various widths, the stack pusher has an adjustable travel length in relation to the width of the stack to be pushed from the platform.
Groups of paper sheets may be delivered from a printing press or another suitable source to various processing or consuming machines via a transporting system, or delivery equipment. A system which intermittently delivers sheets to consuming machines is disclosed by Muller (U.S. Pat. No. 4,235,434). The system includes a group forming device that gaps a continuous, scalloped stream of paper sheets. In the event of a malfunction in a processing or consuming machine, the group of sheets advances along a main path of the transporting system to a surplus receiving unit or overflow. A set of diverter switches drop the sheets into magazines for one or more consuming machines, over separate conveyor belts, or to one or more surplus receiving units. Consuming machines can deliver sheets to or may constitute gathering machines, collating machines, or other types of processing machines. The diverter switches are moved by fluid operated devices. A signal generating sensor, upstream of the switches, is a conventional counter which controls the operation of the group forming device. The group forming device is said to divide the continuous stream of sheets into a single file of discrete groups or streams.
The Muller '434 system uses a group forming device and diverter switches to process multiple stacks. However, the bins for the consuming machines or surplus receiving units do not have any compression means and compensation or rotation means to efficiently process products having one edge thicker than other edges. Moreover, the discrete streams are of identical length and contain identical numbers of partially overlapping sheets. Furthermore, the accumulations of numerous fully or nearly fully overlapping sheets at the leading ends of the discrete streams can interfere with introduction of discrete streams into the magazines of various processing machines.
Frequently when dealing with printed sheets or copies such as newspapers, the number of newspapers to be delivered to a dealer is not always a multiple of the number, e.g., 25, constituting one bundle. A machine to provide bundles containing odd copies, i.e., copies of a number less than 25, is disclosed by Kawada (U.S. Pat. No. 4,302,198). The Kawada machine includes a counter stacker having a counter head for counting copies in a scalloped stream. A first dividing plate, located downstream from the counter, is inserted into the stream (using an air cylinder) to stop subsequent copies. When the disclosed machine is diverting the stream to a second path, a second dividing plate is lowered, the stream is gapped by the first plate, and then the second plate is raised. A first stacking bin, receiving products from a first path, includes a turntable and a pusher. The second stacking bin, receiving products from the second path, includes a pusher.
Kawada discloses using a second stacking bin to accommodate stacks of less than 25 copies. Kawada also indicates that the end structures of the first and second paths may be replaced with each other. However, Kawada does not address consecutively low quantity stacks. Moreover, the machine does not have true modularity in that the first stacking bin is different from the second stacking bin. Furthermore, due to the lack of modularity, the machine is not expandable to more than two stacking bins.
An assembly for selectively transporting a stream of partly overlapping paper sheets or the like from a first path into one of several additional paths is important in the printed paper business. One assembly to prevent the accumulations of fully overlapping sheets at the leading end of discrete streams is disclosed by Muller (U.S. Pat. No. 4,447,052). Muller '052 describes a machine that selectively routes a scalloped stream from a first path to either a second or third path. When the stream is routed from the first path to the second path, a switching device, operated by a double-acting pneumatic cylinder, is lowered over a gap. A blade-like member, controlled by a fluid operated unit, is lowered to form a gap in the stream. At the instant when a sheet has its trailing edge over the switching device, the switching device is raised. Meanwhile the intercepted sheet is allowed to travel down the third path to a magazine of a gathering machine.
The Muller '052 machine uses a switching device to prevent accumulations of fully overlapping sheets at the leading ends of discrete streams. However, Muller only describes one switching device and its interaction with the blade-like member used to form a gap so as to form two streams. Moreover the use of stackers is not described. The machine does not have the ability to do direct stacking of the scalloped stream into successive low quantity stacks.
In a newspaper stacking plant, stacks of less than 17 copies were made by hand. An assembly to enable machine stacking of small stacks (less than 17 copies), including a stack size of one or several copies, is disclosed by Backman (U.S. Pat. No. 4,569,513). The Backman assembly includes an interceptor device that is controlled by a sensor to interrupt a flow of overlapping newspapers. Another interceptor device provides a gap in the flow of newspapers. Pushers push their respective stacks from tables.
Backman discloses a way to create one low quantity (less than 17 copies in this invention) secondary stack. Backman also discusses use of rotation (compensation) on the primary stack. However, the assembly cannot consecutively process two or more, low quantity stacks (under 17 copies). Moreover, the Backman assembly cannot accommodate variablesized products. Additionally, the assembly does not use multiple, modular stacking bins that can compress a stack.
Thus, while the preceding patents discuss a transporting assembly (or delivery equipment) with a device to gap and divide the incoming product stream and a diverter device to send the diverted products down another path, and two of the patents disclose systems using a stackers with a pusher device, none of them address the use of multiple, modular compensating stacking bins and coplanar diverters to produce successive, low quantity stacks of various product sizes.
Consequently there is a need for a modular system having a plurality of compensating stacking bins, diverters, and a single gapper such that successive, low quantity stacks can be produced without slowing, and independent of, the delivery equipment or transporting assembly. There is also a need for such a system to accommodate a variety of product sizes.